Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Patent
1996-12-02
1998-12-22
Dinh, Tan
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
3692754, G11B 1100
Patent
active
058525912
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magneto-optical recording medium and a head unit for a magneto-optical recording medium. Particularly, the present invention relates to a magneto-optical recording medium using a substrate where grooves are formed and also a head unit for a magneto-optical recording medium which compensates the Kerr ellipticity of the magneto-optical recording medium.
BACKGROUND ART
In the magneto-optical disks as a magneto-optical recording medium, grooves for guiding a light beam irradiated to the magneto-optical disk have hitherto been formed concentrically or spirally. At the time of the recording or reproduction of the magneto-optical disk, the tracking control of the light beam irradiated to the magneto-optical disk is performed based on the reflected light from the grooves of the light beam which was irradiated on the magneto-optical disk. As a consequence, in the magneto-optical disk, data is recorded on an area (hereinafter referred to as a land) between grooves at the time of the recording, and data recorded on the land is read out at the time of the reproduction.
Incidentally, in an magneto-optical disk such as this, with the object of enhancing the recording density there has been proposed a magneto-optical disk where signals are recorded on both a groove and a land and thereby a wide recording area is assured. When a magneto-optical disk such as this is reproduced, however, cross talk from nearby grooves or lands becomes a problem.
As a method of reducing this cross talk, there has been proposed an optical method and a signal processing method. In the optical method, three light spots are irradiated on the magneto-optical disk, and when the signal on the groove (or land) is reproduced with the central light spot, the signal on the land (or groove) is reproduced with the light spots before and after, thereby eliminating the cross talk caused by the signal component of the land (or groove) included in the reproduced signal. On the other hand, in the signal processing method, the cross talk included in the reproduced signal can be eliminated by improving the signal-to-noise ratio (SN ratio) of the reproduced signal with Viterbi decoding.
However, in the aforementioned optical method, since three spots are irradiated on the magneto-optical disk and the signals on adjacent lands or grooves are reproduced, there is the problem that the pick-up structure becomes complicated and is increased in size. Also, the signal processing method has disadvantages in that the circuit structure becomes complicated. Thus, either case has still been unsatisfactory from practical use as a solution of eliminating the cross talk.
DISCLOSURE OF INVENTION
The present invention relates to a magneto-optical recording medium and a head unit for a magneto-optical recording medium which solve the aforementioned problems.
In the present invention, a magneto-optical recording medium has a substrate formed from material having light transmittivity and also has a magneto-optical recording film provided on one surface of the substrate. In said one surface of the substrate where the magneto-optical recording film is provided, when a wavelength of a light beam, irradiated to the magneto-optical recording medium, is .lambda., there are formed grooves having an optical depth where its lower limit is .lambda./8 and its upper limit is .lambda./4 or less.
Furthermore, in the present invention, a head unit for a magneto-optical recording medium having a magneto-optical recording film having a Kerr ellipticity of a predetermined value, comprises: a light source; an object lens for focusing a light beam, emitted from the light source, on the magneto-optical recording film of the recording medium; first optical split means for separating a return light reflected from the magneto-optical recording film on which the light beam is incident through the object lens, from the light beam emitted from the light source; second optical split means for splitting the return light reflected from the magneto-optica
REFERENCES:
patent: 5602823 (1997-02-01), Aoki et al.
patent: 5636201 (1997-06-01), Ooki
Dinh Tan
Sony Corporation
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